This invention relates to the field of cleaning the surfaces within pipes. The surfaces may be metal, including stainless steel. The restricted points of entry may prevent these surfaces from being cleaned by application of mechanical force or sonic energy. The contaminants to be cleaned from the surfaces include organic matter and particulates.
The oxygen supply systems on aircraft may comprise oxygen converters, oxygen regulators, molecular sieve oxygen generators (MSOG units), oxygen pipes which are more commonly referred to as oxygen lines, and other apparatus. The cleaning of these oxygen supply systems is required primarily to remove two types of contamination. The first type of contamination arises from organic compounds. These organic compounds include jet fuel, compounds that result from the incomplete combustion of jet fuel, hydraulic oil and special types of greases that are used in these oxygen systems. The second type of contamination arises from particles of dust and dirt, as well as particles of Teflon that are found in the greases that may be used in these oxygen systems, and from Teflon tape which may be used in the threaded connections of these oxygen systems. The particulates may be in a size range of about one to 300 microns, and more commonly, in a size range of about 2 to about 150 microns.
The prior art attempts to clean oxygen lines have involved the use of chlorofluorocarbons, and have generally had unsatisfactory results. Aqueous solvents are unsatisfactory because they are difficult to remove completely and residual water may freeze and create a dangerous buildup of pressure.
There are certain requirements for methods, compositions and apparatus for cleaning the surfaces within aircraft oxygen lines to remove such contaminants. The methods should be able to be carried out in a relatively short period of time. Preferably, the cleaning should be carried out with the minimum removal of components of the oxygen system from the aircraft. The cleaning compositions should be non-aqueous, non-flammable, non-toxic, and environmentally friendly. The solvent of the cleaning compositions should be able to be used as a verification fluid that is circulated through the cleaned components in order to verify cleaning. The apparatus for cleaning should preferably be transportable to the location of the aircraft. The cleaning should achieve at least a level B of ASTM standard G93-96, which may be stated as less than 3 mg/ft2 (11 mg/m2), or less than about 3 mg. of contaminants per square foot of interior surface of the components, or less than about 11 mg. of contaminants per square meter of interior surface of the components. The method of ASTM standard G93-96 may not accurately determine the level of cleanliness in vessels with restricted entry.
There are other installations where clean oxygen lines are required. These include hospitals and physical science research facilities.
The present invention comprises methods, compositions and apparatus for cleaning the interior surfaces of pipes, and particularly, oxygen lines. These methods, compositions and apparatus have certain features in common, and other features that may be varied depending on the nature of the surfaces to be cleaned.
The present invention achieves the satisfactory cleaning of contaminants from pipes by first pulling a vacuum on the pipe to be cleaned. The pipe is then filled with a solvent, which is preferably a fluorocarbon solvent. After the pipe is filled with solvent, a cleaning solution is pumped at a high velocity through the pipe. The cleaning solution preferably comprises the fluorocarbon solvent, and a fluorosurfactant. The pipe is then rinsed with solvent. A particle counter is used to determine whether the solvent rinse contains an acceptably low number of particles. The solvent is then blown out of the pipe by a gas, such as dry air. A vacuum is then pulled on the pipe to evaporate the solvent. Subsequently, a hot dry gas is pumped through the pipe to remove any remaining solvent. The gas is preferably hot, dry air. The gas exiting from the pipe is then checked with a halogen detector to confirm that it contains an acceptably low level of solvent vapor.